Field of the Invention
The invention relates to a separator for separating tobacco particles from a tobacco/gas mixture comprising a hood, a circular deflection space arranged in the hood, an inlet for the tobacco/gas mixture to be separated opening tangentially into the circular deflection space, a downwardly directed outlet in the deflection space for the tobacco particles, an outlet for the tobacco particles at the lower end of the hood, and an outlet for the gas above the deflection space.
In the course of tobacco processing, in particular, however, in the treatment of expanded tobacco, the production of which is apparent for example from U.S. Pat. No. 4,844,101, the tobacco particles must be separated from the produced tobacco/gas mixture. In particular for the expansion of tabacco steam or vapour is often used, and consequently hereinafter the term "gas" is intended to cover vaporous media as well.
The basic principles of particle separation by mass forces will be found, for example, in "Ullmanns Enzyklopaedie der Technischen Chemie", 4th edition volume 2, Process Technology I. Such "separators" have also already been used in the tobacco industry. Thus, German Offenlegungsschrift No. 3.619,816 discloses an apparatus for expanding tobacco which includes, apart from a cyclone dust separator, a separator having a mesh screen. The mesh screen permits the passage of the steam/air mixture to an outlet tube which supplies it to the cycle again, whilst the tobacco particles are led downwardly to an air lock.
European patent application No. 29,588 discloses a method for heating tobacco impregnated with an expansion agent in which the expanded-tobacco-containing gas is separated from the tabacco particles by means of a tangential separator.
A separator as acknowledged above for separating dust particles from a gas is disclosed in German patent specification No. 639,871. In this case to the inlet an annular passage is connected from the bottom of which several passages lead downwardly in helical windings turning in the same direction as the crude gas supply conduit and terminating with gradual translation at the chamber wall into a chamber disposed beneath the annular passage; the radius of curvature of these passages is smaller than the radius of the hood.
This is thus an embodiment of a centrifugal force separator in which the mixture streams must be conveyed with relatively high speed to obtain the desired separation caused by the change of movement on passing through the curved passages.
A disadvantage here is the relatively great constructural requirements needed for the apparatus for the necessary high transport speed both in the inlet and in the deflection space and finally in the hood; moreover, for satisfactory operation of this separator it is absolutely essential for all areas coming into contact with the dust/gas mixture, in particular the helically curved passages, to be kept carefully clean because depositions on the walls thereof, in particular encrusted particles, immediately lead to impairment of the separation efficiency. Finally, the lower end of the hood must be kept closed, for example, by a rotary vane lock to ensure the necessary high conveying speeds. There are, however, many used where the operation can or must be carried out with an open outlet.